linux-kernel - Re: [PATCH 1/2] Define find_symbol_in_section

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Date:	Wed, 15 Jul 2015 13:31:26 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Minfei Huang <mhuang@...hat.com>, rob.jones@...ethink.co.uk,
	amhyung@...nel.org, linux-kernel@...r.kernel.org,
	Minfei Huang <mnfhuang@...il.com>
Subject: Re: [PATCH 1/2] Define find_symbol_in_section_t as function type to
 simplify the code

On Wed, 15 Jul 2015 07:22:32 +0930 Rusty Russell <rusty@...tcorp.com.au> wrote:

> Minfei Huang <mhuang@...hat.com> writes:
> > From: Minfei Huang <mnfhuang@...il.com>
> >
> > It is not elegance, if we use function directly as the argument, like
> > following:
> >
> > bool each_symbol_section(bool (*fn)(const struct symsearch *arr,
> >                                    struct module *owner,
> >                                    void *data), void *data);
> >
> > Here introduce a type defined function find_symbol_in_section_t. Now
> > we can use these type defined function directly, if we want to pass
> > the function as the argument.
> >
> > bool each_symbol_section(find_symbol_in_section_t fn, void *data);
> 
> I disagree.
> 
> It's shorter, but it's less clear.  typedefs on functions are not very
> useful:
> 1) They require readers to look in two places to see how to use the
>    function (ie each_symbol_section).
> 2) They can't use the typedef to declare their function, since that
>    doesn't work in C.
> 
> If the function were being used many times, it makes sense.  But
> it's only used twice, once static inside module.c.
> 

Using a foo_t typedef for a function callback is a common pattern. 
It's (almost) the only approved use of typedefs.  The usage is
widespread enough that when one sees a foo_t type, one says "ahah,
that's a function pointer".

Sorry, but I don't think "Rusty doesn't like it" is a good reason for
the module code to be different.  All of us dislike some aspects of
kernel coding practices, but we go along because consistency is more
important.

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